Question 1

When copper is left in moist air for a long time, it develops a green coating because of:

Accepted Answer

a layer of basic copper carbonate forming on the copper surface. Copper reacts with moisture and carbon dioxide in the air over time, leading to the formation of basic copper carbonate, which gives the characteristic green patina. This process is a result of copper's corrosion in the presence of these elements.

Question 2

Why is chlorine commonly added during water treatment?

Accepted Answer

to destroy disease-causing microbes. Chlorine is added to water to kill disease-causing microorganisms (disinfection), not to raise dissolved oxygen.

Question 3

Which of the following is classified as a primary pollutant?

Accepted Answer

CO. CO is a primary pollutant (emitted directly from incomplete combustion). H2SO4, PAN and aldehydes are secondary pollutants formed in the atmosphere, so the stored H2SO4 is wrong.

Question 4

In automobile exhaust, which of the following are considered harmful pollutants?
(i) N2
(ii) CO
(iii) CH4
(iv) Oxides of nitrogen

Accepted Answer

(ii) and (iv). Carbon monoxide (CO) and oxides of nitrogen are harmful pollutants found in automobile exhaust, as they contribute to air pollution and can have serious health effects. In contrast, nitrogen (N2) is a non-toxic gas that makes up a large portion of the atmosphere, and methane (CH4) is not a direct product of combustion in typical vehicle exhaust.

Question 5

If rainfall occurs together with a thunderstorm, the pH of the rainwater collected will be

Accepted Answer

a little lower than the pH of rainwater falling without a thunderstorm. Thunderstorms often produce more acidic rain due to the presence of lightning, which can convert nitrogen in the atmosphere into nitrogen oxides that dissolve in rainwater, lowering its pH compared to rain without a thunderstorm.

Question 6

Photochemical smog is most likely to form during which condition?

Accepted Answer

summer in the daytime. Photochemical smog forms when sunlight triggers chemical reactions between pollutants, which is most prevalent during the summer when temperatures are higher and sunlight is abundant, particularly during the daytime.

Question 7

The B.O.D. (biochemical oxygen demand) test is used to assess the level of

Accepted Answer

water contamination. The B.O.D. test measures the amount of oxygen consumed by microorganisms in water as they decompose organic matter, making it a key indicator of water contamination levels.

Question 8

Smog is mainly due to the presence of which pair of gases?

Accepted Answer

Oxides of sulphur and nitrogen. Smog is caused by oxides of sulphur (classical) and nitrogen (photochemical), not by the oxygen and nitrogen of normal air.

Question 9

Which statement correctly describes ozone-layer depletion?

Accepted Answer

Ozone depletion is more severe near the poles because ice crystals in polar clouds catalyze photochemical reactions that break down ozone through Cl• and ClO• radicals.. The correct option highlights that the unique conditions in polar regions, including the presence of ice crystals in polar stratospheric clouds, facilitate reactions that release chlorine radicals, which are highly effective in breaking down ozone molecules, leading to greater depletion compared to other areas.

Question 10

The stratospheric ozone layer needs safeguarding against the unchecked use of which of the following?

Accepted Answer

aerosols and high-flying jets. The stratospheric ozone layer is endangered by chlorofluorocarbons from aerosols and by oxides of nitrogen from supersonic/high-flying jets. Pesticides do not deplete stratospheric ozone.

Question 11

Thermal pollution primarily has its impact on which of the following?

Accepted Answer

aquatic organisms. Thermal pollution mainly affects aquatic organisms because it alters the temperature of water bodies, which can disrupt the delicate balance of ecosystems, harm fish and other aquatic life, and reduce oxygen levels in the water.

Question 12

Sewage water is cleaned mainly by the action of

Accepted Answer

micro-organisms. Micro-organisms play a crucial role in the sewage treatment process by breaking down organic matter and pollutants, effectively purifying the water through biological decomposition.

Question 13

Why is carbon monoxide (CO) dangerous to humans?

Accepted Answer

It binds to haemoglobin and competes with oxygen. CO is dangerous because it binds haemoglobin much more strongly than oxygen, forming carboxyhaemoglobin and starving tissues of O2. It is not a carcinogen.

Question 14

Identify the statement that is incorrect.

Accepted Answer

Rainwater is termed acid rain when its pH is above 6.5.. Option D is incorrect because rainwater is classified as acid rain when its pH is below 5.6, not above 6.5, indicating a higher acidity level.

Question 15

Repeated appearance of algal blooms in a lake is a sign of

Accepted Answer

high availability of nutrients. Recurrent algal blooms indicate a high availability of nutrients (N, P) - eutrophication. The stored 'no herbivores' is not the cause.

Question 16

Which of the following is not usually present as a constituent of photochemical smog?

Accepted Answer

Chlorofluorocarbons. Photochemical smog contains ozone, PAN, acrolein, NOx and aldehydes. Chlorofluorocarbons are stratospheric pollutants, not smog constituents - so CFCs are the odd one out, not ozone (which is a major smog component).

Question 17

Which of the following acts as a reservoir for carbon dioxide (CO2)?

Accepted Answer

Oceans. Oceans act as a significant reservoir for carbon dioxide because they absorb large amounts of CO2 from the atmosphere, helping to regulate global carbon levels and influence climate.

Question 18

A tooth disorder marked by mottled enamel is caused by the presence of which chemical element in drinking water?

Accepted Answer

Fluorine. Mottled tooth enamel is caused by excess fluorine (fluoride) in drinking water (dental fluorosis), not boron.

Question 19

Minamata disease results from contamination of which medium?

Accepted Answer

mercury from industrial effluents entering fishing waters. Minamata disease is caused by mercury poisoning, specifically from industrial waste that contaminates water bodies, leading to the accumulation of mercury in fish, which then affects human health when consumed.

Question 20

Select the sequence of True (T) and False (F) for the following statements:
(1) Rainwater is termed acid rain when its pH falls below 3.6.
(2) The ozone hole over Antarctica is most pronounced during September–October and is restored during November–December.
(3) Methylcyclohexane is a sub

Accepted Answer

FTFT. The correct option is right because statement (1) is false; acid rain is typically defined as rain with a pH below 5.6. Statement (2) is true as the ozone hole is indeed most pronounced during September–October. Statement (3) is false because methylcyclohexane does not deplete ozone; it is not an ozone-depleting substance. Statement (4) is true since COD is generally higher than BOD due to the inclusion of both biodegradable and non-biodegradable organic matter.

Question 21

If rainfall occurs together with a thunderstorm, what happens to the pH of the collected rainwater?

Accepted Answer

It becomes slightly lower than the pH of rainwater falling without a thunderstorm. During a thunderstorm, lightning can produce nitrogen oxides, which dissolve in rainwater and form nitric acid, leading to a decrease in pH. This results in the rainwater being more acidic compared to rain that falls without a thunderstorm.

Question 22

Smog is mainly due to the presence of which of the following?

Accepted Answer

Oxides of sulphur and nitrogen. Smog is primarily caused by the chemical reactions between oxides of sulfur and nitrogen, which are released from industrial processes and vehicle emissions, leading to the formation of particulate matter and other pollutants that contribute to smog.

Question 23

Select the incorrect statement from the following set:

Accepted Answer

The ozone layer blocks infrared radiation from the Sun from reaching Earth. The ozone layer primarily absorbs harmful ultraviolet (UV) radiation, not infrared radiation, which is why this statement is incorrect.

Question 24

Choose the statement that is not correct among the following.

Accepted Answer

Ozone is responsible for absorbing infrared radiation.. Ozone primarily absorbs ultraviolet radiation, not infrared radiation, making this statement incorrect.

Question 25

DDT is classified as which of the following?

Accepted Answer

A pollutant that does not biodegrade readily. DDT is a synthetic pesticide that persists in the environment for long periods, accumulating in the tissues of living organisms and not breaking down easily, which classifies it as a pollutant.

Question 26

A sample of water taken from an underground lake was analyzed and found to contain fluoride, lead, nitrate, and iron at concentrations of 1000 ppb, 40 ppb, 100 ppm, and 0.2 ppm, respectively. This water is unfit for drinking because of the elevated level of:

Accepted Answer

Nitrate. Nitrate levels above 10 ppm can pose serious health risks, particularly for infants, as they can interfere with oxygen transport in the blood. The concentration of 100 ppm in this sample significantly exceeds safe drinking water standards, making it the primary concern.

Question 27

A water sample contains the following anions at ppm concentrations: F− = 10, SO4²− = 100, and NO3− = 50. Which of these anion(s) make the sample unfit for drinking?

Accepted Answer

Only F−. Fluoride (F−) at elevated levels can pose health risks, particularly to dental health, making the water sample unfit for drinking. While nitrate (NO3−) can also be harmful at high concentrations, the level of fluoride in this sample is specifically noted as a concern.

Question 28

A water sample contains the following metal concentrations in ppm: Fe = 0.2, Mn = 5.0, Cu = 3.0, and Zn = 5.0. Which metal is responsible for making the sample unfit for drinking?

Accepted Answer

Mn. Manganese (Mn) at a concentration of 5.0 ppm exceeds the acceptable limits for drinking water, which can lead to health issues, making it the metal responsible for rendering the sample unfit for consumption.

Question 29

What is the likely consequence of an excessive increase in atmospheric carbon dioxide levels?

Accepted Answer

rise in global temperatures. An excessive increase in atmospheric carbon dioxide levels enhances the greenhouse effect, trapping more heat in the Earth's atmosphere, which leads to a rise in global temperatures.

Question 30

Assertion: Nitrogen and oxygen are the main components in the atmosphere but these do not react to form oxides of nitrogen.
Reason: The reaction between nitrogen and oxygen requires high temperature.

Accepted Answer

Both assertion and reason are correct, and the reason is the correct explanation for the assertion. The assertion is true because nitrogen and oxygen are indeed the primary gases in the atmosphere, and they typically do not react under normal conditions. The reason is also accurate, as the formation of nitrogen oxides requires high temperatures, such as those found in combustion processes, which explains why these gases do not react under standard atmospheric conditions.

Question 31

Biochemical oxygen demand (BOD) value can be a measure of water pollution caused by organic matter. Which of the following statements is correct ?

Accepted Answer

Polluted water has BOD value higher than 10 ppm. BOD measures oxygen demand from organic pollution. Clean water has BOD <= 5 ppm, while polluted water has BOD higher than 10 ppm (often 17 ppm or more). Aerobic bacteria do not decrease BOD, and anaerobic bacteria do not increase it. So the correct statement is that polluted water has BOD value higher than 10 ppm.

Question 32

The higher concentration of which gas in air can cause stiffness of flower buds ?

Accepted Answer

SO2. Sulfur dioxide (SO2) can lead to physiological stress in plants, causing symptoms such as stiffness in flower buds due to its toxic effects on plant tissues and disruption of normal growth processes.

Question 33

A water sample has ppm level Fe = 0.2; Mn = 5.0; Cu = 3.0; Zn = 5.0. The metal that makes the water sample unsuitable for drinking is:

Accepted Answer

Mn. Drinking-water limits (ppm): Fe ~0.3, Cu ~1-3, Zn ~5, but Mn ~0.05-0.1. Mn = 5.0 ppm exceeds its limit by ~50-100x, making the water unsuitable. Answer: Mn.

Question 34

Air pollution that occurs in sunlight is: (1) oxidising smog (2) reducing smog (3) fog (4) acid rain

Accepted Answer

(1) oxidising smog. Oxidising smog, also known as photochemical smog, forms when sunlight reacts with pollutants like nitrogen oxides and volatile organic compounds, leading to the production of ozone and other harmful substances in the atmosphere.

Question 35

The correct set of species responsible for the photochemical smog is:

Accepted Answer

NO, NO2, O3 and hydrocarbons. The correct option includes nitrogen oxides (NO and NO2), ozone (O3), and hydrocarbons, which are key components in the formation of photochemical smog through complex reactions driven by sunlight.

Question 36

The primary pollutant that leads to photochemical smog is:
(1) acrolein
(2) ozone
(3) sulphur dioxide
(4) nitrogen oxides

Accepted Answer

nitrogen oxides. Nitrogen oxides are the main contributors to the formation of photochemical smog, as they react with sunlight and volatile organic compounds to produce ozone and other harmful pollutants.

Question 37

The layer of atmosphere between 10 km to 50 km above the sea level is called as: (1) troposphere (2) thermosphere (3) stratosphere (4) mesosphere

Accepted Answer

stratosphere. The region of the atmosphere from about 10 km to 50 km above sea level is the stratosphere (it contains the ozone layer); the mesosphere lies above it, roughly 50-85 km.

Question 38

Which is wrong with respect to our responsibility as a human being to protect our environment?
(1) Restricting the use of vehicles
(2) Avoiding the use of floodlighted facilities
(3) Setting up compost tin in gardens
(4) Using plastic bags

Accepted Answer

Using plastic bags. Using plastic bags is the environmentally harmful (wrong) practice. Restricting vehicle use, avoiding floodlighting, and composting are all responsible, eco-friendly actions.

Question 39

The reaction that is NOT involved in the ozone layer depletion mechanism in the stratosphere is:

Accepted Answer

CH4 + 2O3 -> 3CH2 = O + 3H2O. ClO+O->Cl+O2, CF2Cl2 photolysis to Cl, and HOCl photolysis to OH+Cl are all genuine ozone-depletion steps. The reaction CH4 + 2O3 -> 3CH2=O + 3H2O (also unbalanced/fictitious) is not part of the mechanism.

Question 40

The compound that is NOT a common component of photochemical smog is

Accepted Answer

CF2Cl2. Common photochemical-smog components include ozone (O3), PAN (CH3C(O)OONO2) and acrolein (CH2=CHCHO). CF2Cl2 is a chlorofluorocarbon refrigerant, not a smog constituent.

Question 41

Thermal power plants can lead to-

Accepted Answer

Acid rain. Thermal power plants burn fossil fuels releasing SO2 and NOx, which form sulfuric and nitric acids in the atmosphere, causing acid rain.

Question 42

The incorrect statement(s) among (a) – (d) regarding acid rain is (are):
(a) It can corrode water pipes
(b) It can damage structures made up of stone
(c) It cannot cause respiratory ailments in animals
(d) It is not harmful for trees

Accepted Answer

(2) (c) and (d). Statements (c) 'cannot cause respiratory ailments' and (d) 'not harmful for trees' are false, since acid rain causes respiratory problems and damages vegetation; (a) corroding pipes and (b) damaging stone are true. So the incorrect statements are (c) and (d).

Question 43

The condition that indicates a polluted environment is

Accepted Answer

eutrophication. BOD of 5 ppm, 0.03% CO2, and rain pH 5.6 are all normal/clean conditions. Eutrophication (nutrient over-enrichment causing algal blooms and oxygen depletion) is the indicator of a polluted environment. Correct option: eutrophication.

Question 44

Among the gases (a) – (e), the gases that cause greenhouse effect are: (a) CO2 (b) H2O (c) CFCs (d) O2 (e) O3

Accepted Answer

(a), (b), (c) and (e). Carbon dioxide (CO2), water vapor (H2O), chlorofluorocarbons (CFCs), and ozone (O3) are all known to trap heat in the atmosphere, contributing to the greenhouse effect, while oxygen (O2) does not have this property.

Question 45

Biochemical Oxygen Demand (BOD) is the amount of oxygen required in ppm:
(1) for the photochemical breakdown of waste present in 1 m³ volume of a water body.
(2) for sustaining life in a water body.
(3) by bacteria to break-down organic waste in a certain volume of a water sample.
(4) by a

Accepted Answer

(3). Biochemical Oxygen Demand (BOD) specifically measures the amount of oxygen that bacteria require to decompose organic matter in a water sample, making option (3) the correct choice.

Question 46

Given below are two statements:
Statement I: An allotrope of oxygen is an important intermediate in the formation of reducing smog.
Statement II: Gases such as oxides of nitrogen and sulphur present in troposphere contribute to the formation of photochemical smog.
In the light of the above

Accepted Answer

Both statement I and Statement II are false. Both statements are incorrect because the primary allotrope of oxygen involved in smog formation is ozone, which is not a direct intermediate in reducing smog, and while nitrogen oxides and sulfur oxides do contribute to smog, they are more associated with traditional smog rather than photochemical smog.

Question 47

Given below are two statements:
Statement I:
The pH of rain water is normally ~5.6.
Statement II:
If the pH of rain water drops below 5.6, it is called acid rain.
In the light of the above statements, choose the correct answer from the options given below:

Accepted Answer

Both Statement I and Statement II are true.. Rainwater typically has a pH of around 5.6 due to the presence of dissolved carbon dioxide, which forms carbonic acid. When the pH falls below this level, it indicates an increase in acidity, thus classifying it as acid rain.

Question 48

Which one of the following statements is NOT correct ?

Accepted Answer

Eutrophication leads to increase in the oxygen level in water. Eutrophication typically results in an overgrowth of algae, which can deplete oxygen levels in the water as the algae die and decompose, leading to hypoxic or anaerobic conditions rather than an increase in oxygen.

Question 49

Match List - I with List - II:
List – I (compound)
(a) Carbon monoxide
(b) Sulphur dioxide
(c) Polychlorinated biphenyls
(d) Oxides of Nitrogen
List – II (effect/affected species)
(i) Carcinogenic
(ii) Metabolized by pyrus plants
(iii) Haemoglobin
(iv) Stiffness of flower buds
Choose the c

Accepted Answer

(a) - (iii), (b) - (iv), (c) - (i), (d) - (ii). CO binds haemoglobin (iii); SO2 causes stiffness of flower buds (iv); polychlorinated biphenyls are carcinogenic (i); oxides of nitrogen are metabolized by Pyrus plants (ii). So (a)-iii,(b)-iv,(c)-i,(d)-ii (index 0).

Question 50

BOD values (in ppm) for clean water (A) and polluted water (B) are expected respectively:

Accepted Answer

A < 5, B > 17. Clean water typically has very low BOD values, indicating minimal organic pollution, while polluted water has higher BOD values due to the presence of organic matter that consumes oxygen.

JEE Main Chemistry: Environmental Chemistry questions with solutions

Questions